Intramuscular Ganglion Cyst of the Extensor Digitorum Longus

Ganglion cyst is a mucin-filled synovial cyst. It is the most common mass found in the wrist and hand. However, it is less commonly encountered in the lower extremity and even rarer to be found intramuscularly.

A 34-year-old female presented for a symptomatic mass at the anterolateral left knee. Radiography revealed an intramuscular multiseptated cystic lesion within the extensor digitorum longus muscle. No definite solid components or enhancement of the lesion and no intra-articular extension or capsular communication were observed. Differential diagnosis included intraosseous myxoma and atypical ganglion cyst with inability to exclude malignancy. The patient underwent an open excisional biopsy that corresponded to a ganglion cyst on histopathological assessment.

Intramuscular ganglion cysts are rare and underreported in the literature. A thorough differential diagnosis for lesions in uncommon anatomical locations is essential. Surgical excision with histological confirmation remains crucial for diagnostic and therapeutic purposes to rule out malignancy and prevent recurrence.